¹₉ of the visitors at a park were boys. 70% of the remaining visitors were girls and the rest were adults. The total number of boys and adults is 187 less than the number of girls. After some girls entered the park, 80% of the visitors that remained were girls. How many girls entered the park?

Boys	Adults	Girls	Total
1x5	8x5		9x5
	3x4	7x4
5	12	28	45

	Boys and adults	Girls
Before	17x1 = 17 u	28x1 = 28 u
Change		+ 40 u
After	1x17 = 17 u	4x17 = 68 u

70% = ⁷⁰₁₀₀ = ⁷₁₀
Adults : Girls = 3 : 7

The total number of adults and girls at first is repeated.  Make the total number of adults at first the same. LCM of 8 and 10 is 40.

80% = ⁸⁰₁₀₀ = ⁴₅

When some girls entered, the total number of boys and adults remains unchanged. Make the total number of boys and adults the same. LCM of 17 and 1 is 17.

The total number of boys and adults is 187 less than the number of girls.

Number of less boys and adults than the number of girls at first
= 28 u - 17 u
= 11 u

11 u = 187

1 u = 187 ÷ 11 = 17

Number of girls who entered the park
= 68 u - 28 u
= 40 u
= 40 x 17
= 680

Answer(s): 680